Vented Pressurized Gas-Powered Actuator

ABSTRACT

A vented pressurized gas-powered actuator includes a housing having a central longitudinal axis and an inner surface. The inner surface has a constant radius between first and second planes extending perpendicular to the axis. At least one vent groove extends from the inner surface in a direction away from the axis. The at least one groove has a first end intersecting the first plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.Nos. 61/832,553, filed on Jun. 7, 2013, and 61/835,515, filed on Jun.14, 2013, the disclosures of which are incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

The embodiments described herein generally relate to a vented,pressurized gas-powered actuator and methods and structured usable forcontrolling an actuation force profile of the actuator.

Various types of actuators may be used to automatically move certainportions of vehicles. These actuators may be configured to exert a forcewithin a predetermined range, or to move elements or the vehicle adesired distance or along a predetermined path. Some actuator designsutilize a piston and an attached piston rod powered by a pressurizedfluid, such as a pressurized gas. It is desirable to be able to controlthe force exerted by the actuator according to the position of thepiston or piston rod during various portions of the piston rod stroke.

SUMMARY OF THE INVENTION

In one aspect of the embodiments described herein, a vented pressurizedgas-powered actuator is provided. The actuator includes a housing havinga central longitudinal axis and an inner surface. The inner surface hasa constant radius between first plane and second planes extendingperpendicular to the axis. At least one vent groove extends from theinner surface in a direction away from the axis. The at least one groovehas a first end intersecting the first plane.

In another aspect of the embodiments of the described herein, a ventedpressurized gas-powered actuator housing is provided. The housingincludes an inner surface and at least one vent groove extending fromthe inner surface into the wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of one embodiment of a ventedpressurized gas-powered actuator prior to activation of the actuator.

FIG. 2 is a cross-sectional side view of the actuator housing shown inFIG. 1 after activation of the actuator.

FIG. 3 is a cross-sectional end view of a housing incorporating a singlevent groove as shown in the embodiment of FIGS. 1 and 2.

FIG. 4 is a cross-sectional side view of the housing embodiment shown inFIGS. 1-3.

FIG. 5 is a partial perspective view of a portion of an exterior of thehousing shown in FIGS. 1 and 2.

FIG. 6 is a perspective end view of the housing shown in FIG. 5.

FIG. 7 shows a cross-sectional end view of a portion of an actuatorincluding a housing having two diametrically opposed vent grooves,similar to the groove 12 v shown in FIG. 3.

FIG. 7A is a schematic view of a housing incorporating the vent groovearrangement shown in FIG. 7.

FIG. 8 shows a cross-sectional end view of a portion of an actuatorincluding a housing having a single vent groove as shown in FIGS. 1-6.

FIG. 9 is a cross-sectional side view of a portion of a housingincorporating an embodiment of a vent groove having a varyingcross-sectional area.

FIG. 10 is a cross-sectional side view of a portion of a housingincorporating another embodiment of a vent groove having a varyingcross-sectional area.

FIG. 11 is a cross-sectional side view of a portion of a housingincorporating another embodiment of a vent groove having a varyingcross-sectional area.

FIG. 12 is a cross-sectional side view of a portion of a housingincorporating another embodiment of a vent groove having a varyingcross-sectional area.

FIG. 13 is a cross-sectional side view of a portion of a housingincorporating another embodiment of a vent groove having a varyingcross-sectional area.

FIG. 14 shows a cross-sectional end view of a portion of an actuatorincluding a housing having three angularly equally spaced vent grooves.

FIG. 14A shows a schematic view of a housing incorporating the ventgroove arrangement shown in FIG. 14.

FIG. 15 is a schematic view of another actuator housing embodimentincorporating an alternative vent groove arrangement.

FIG. 16 is a schematic view of another actuator housing embodimentincorporating an alternative vent groove arrangement.

FIG. 17 is a schematic view of another actuator housing embodimentincorporating an alternative vent groove arrangement.

FIG. 18 shows a plot of force exerted by the piston rod vs. displacementof the piston in the negative Y direction for one example of theembodiment shown in FIGS. 1-6.

FIGS. 19A-C are cross-sectional schematic views showing one embodimentof the progression of formation of a vent groove in a wall of anactuator housing.

FIG. 20 is a cross-sectional side view of a portion of a housingincorporating an exemplary vent groove, showing the basic principle ofoperation of the embodiments described herein.

FIG. 20A shows a cross-sectional side view of a portion of a housingincorporating a particular embodiment of the vent groove as shown inFIGS. 1-6.

FIG. 21A is a cross-sectional side view of a housing incorporating avent groove in accordance with another embodiment described herein.

FIG. 21B is a cross-sectional end view of the housing shown in FIG. 21A.

FIG. 22A is a cross-sectional side view of a housing incorporating avent groove in accordance with another embodiment described herein.

FIG. 22B is a cross-sectional end view of the housing shown in FIG. 22A.

FIG. 23 is a schematic view of a portion of a pedestrian protectionsystem installed in a vehicle and incorporating a hood-lifting deviceaccordance with an embodiment described herein.

DETAILED DESCRIPTION

Like reference numerals refer to like parts throughout the descriptionof several views of the drawings. In addition, while target values arerecited for the dimensions of the various features described herein, itis understood that these values may vary slightly due to such factors asmanufacturing tolerances, and also that such variations are within thecontemplated scope of the embodiments described herein.

FIGS. 1-22 show various embodiments of a vented pressurized gas-poweredactuator, generally designated 10. The actuator 10 may be operativelycoupled (via piston rod 50, described in greater detail, below) to anysuitable device or mechanism for transmitting a force to the device ormechanism. The actuation force is generated responsive to theintroduction of a pressurized gas into a housing of the actuator, in amanner described below. The pressurized gas may be generated within thehousing (for example, by a gas generator incorporated into the housing),or the gas may be introduced into the housing from an external gassource in fluid communication with the housing interior. One possibleapplication for an actuator as described herein is in lifting a portionof a hood of an automotive vehicle.

Any of the elements of any embodiment of an actuator described hereinmay be formed from any suitable material or materials. For example,housing 12 may be formed from a metallic material (for example,stainless steel), a polymer, or any other suitable material ormaterials.

In the embodiment shown in FIGS. 1-6, actuator 10 has a housing 12, apiston 30 slidably positioned within the housing, and a piston rod 50attached to the piston so as to move in conjunction with the piston. Inthe embodiment shown, housing 12 is cylindrical and has an outermosthousing wall 12 d defining a first end 12 a, a second end 12 b and abody 12 c connecting the first and second ends. Wall 12 d also defines ahollow interior 12 e of the housing. In the embodiment shown in FIGS.1-6, housing first end 12 a is flared radially outwardly to accommodatea suitable gas generator 14 (for example, a known micro-gas generator)to be inserted and retained therein by crimping, adhesive attachment, orany other suitable method. Alternatively, the gas generator 14 may beattached to housing first end using a suitable retention method. Agas-emitting portion 14 a of the gas generator 14 is positioned withinthe housing so that generated gases flow into the housing interior 12 eafter activation of the gas generator. If desired, a suitable seal (suchas an epoxy seal, O-ring seal or other sealing means; not shown) may beprovided to prevent or minimize leakage of generated gas between the gasgenerator 14 and the housing 12 to an exterior of the housing.

An interior surface 12 w of wall 12 d has a constant radius measuredfrom housing central longitudinal axis L1 and is structured to permitsliding engagement of a resilient seal 40 therealong, as described ingreater detail below. Seal 40 is mounted on a piston 30. In theembodiments shown in herein, housing inner surface 12 w defines acylindrical volume, and the vent groove(s) described herein resideoutside but adjacent to this cylindrical volume.

In the embodiment shown in FIGS. 1-6, housing second end 12 b has anopening 12 f structured to receive therethrough a piston rod 50 attachedto a piston 30 (described in greater detail below) which is slidablypositioned in housing interior 12 e. Opening 12 f may be sized orotherwise structured to laterally constrain or support to the piston rod50 as portions of the rod move into and out of the housing throughopening 12 f. In the particular embodiment shown in FIGS. 1-6, an endwall 12 g is formed from a portion of housing 12, and opening 12 f isdrilled or otherwise formed in the wall 12 g. If desired, a reinforcingcap (not shown) may be secured to end 12 b of the housing by welding orany other suitable means, to strengthen the housing end against impactforces exerted by the piston 30 contacting the end wall 12 g at the endof the piston stroke.

Piston 30 is slidably positioned within housing interior 12 e. Referringto FIGS. 1 and 2, piston has a base 30 a with an outer wall 30 b. Agroove 30 c is formed in wall 30 b and is structured for receivingtherein a resilient gas-tight seal 40 (for example, a suitable O-ring).In a known manner, seal 40 resiliently engages or contacts the interiorsurfaces of housing wall 12 d, thereby providing a substantiallygas-tight seal between the piston 30 and wall 12 d. When piston 30 ispositioned in housing 12 with seal 40 contacting the housing wallinterior surfaces, the region of contact between the seal and thehousing wall defines a boundary between a higher pressure side P1 of thepiston and a lower pressure side P2 of the piston. Thus, venting willoccur through groove(s) 12 v (described in greater detail below) as longas gases traveling along the groove(s) pass under the seal 40 (betweenthe seal and the housing wall) from the higher pressure side P1 to thelower pressure side P2 side of the piston.

In the embodiment shown in FIGS. 1-6, a projection 30 d extends frompiston base 30 a. Projection 30 d is structured for engaging (or forsuitable attachment to) an associated piston rod 50 in an interferencefit, or for otherwise enabling or facilitating attachment of the pistonrod 50 to the piston 30.

In a particular embodiment, a cavity 30 e is formed in base 30 a. Cavity30 e provides a void space in the piston which is structured toaccommodate therein debris or loosened portions of gas generator 14 (forexample, petalled portions of the gas generator) resulting fromactivation of the gas generator and expulsion of the generated gases),and to confine the initial expansion of the generated gases. This canenable a relatively smaller quantity of gas generant to be used in thegas generator to produce a given effect.

Piston rod 50 is the mechanism through which the actuator force istransmitted to an element (for example, a portion of a hood of a vehicle(shown schematically as element 902 in FIG. 23)) connected to the pistonrod. Piston rod 50 has a first end 50 a attached to the piston so as tomove in conjunction with the piston. A second end 50 b of the piston rodopposite the first end may be configured for attachment to an element ormechanism to which the actuator force is to be transmitted. In theembodiment shown in FIGS. 1-6, piston rod 50 is hollow. Alternatively,the piston rod may be solid, or the piston and piston rod may be formedintegrally with each other, as a single piece. The piston rod may alsohave any particular length, diameter, shape and/or othercharacteristic(s) suitable or necessary for a particular application.

Referring to FIGS. 1-6, at least one vent groove 12 v is formed alonginner surface 12 w of housing wall 12 d. In the embodiment shown inFIGS. 1-6, groove 12 v is produced by a forming operation which pressesa portion 12 x of the housing wall outwardly, in a direction away fromaxis L1 and inner wall surface 12 w and into the wall thickness, so asto outwardly stretch or deform an associated portion of the wall. Thegroove 12 v is formed as the stretched portion 12 x of the wall 12 d ispushed outward. In the embodiments described herein, the vent grooves(with the exception of embodiments of groove 12 k shown in FIGS.21A-22B) extend parallel to housing longitudinal axis L1.

In the embodiment shown in FIGS. 1-6, groove 12 v has a first end 12 v-aintersecting a first plane s1 extending perpendicular to the axis L1,and a second end 12 v-b spaced apart from a second plane s2 extendingperpendicular to the axis. Planes s1 and s2 schematically represent thelongitudinal ends or limits of the constant radius portions of thehousing interior surface 12 w, along which venting from the higherpressure piston side P1 to the lower pressure side P2 may be enabled byproviding vent grooves along the housing. That is, inner surface 12 w(except for the portions along the vent grooves) is located at aconstant radius from axis L1 between planes s1 and s2. The piston movesin direction V, with the piston stroke beginning at or about plane s1and ending at or about plane s2. In the embodiment shown, it is alsoseen that planes s1 and s2 extend through the inner surface 12 w andperpendicular to longitudinal axis of the vent groove.

In the embodiments described herein, planes s1 and s2 also schematicallyrepresent the longitudinal ends or limits of the constant radiusportions of the housing interior surface 12 w along which venting fromthe higher pressure piston side P1 to the lower pressure side P2 may beenabled by providing vent grooves along the housing. That is, innersurface 12 w (except for the portions along the vent grooves) is locatedat a constant radius from axis L1 between planes s1 and s2. The pistonmoves in direction V as shown in FIGS. 1-4, with the piston strokebeginning at or about plane s1 and ending at or about plane s2. Ventingoccurs along grooves formed into surface 12 w.

FIGS. 19A-C show the progression of formation of a vent groove 12 vstarting from an end of housing body portion 12 c, using one possiblegroove formation method. In the embodiment shown, a forming tool 800 isshaped so as to produce a groove having a the desired shape anddimensions, by displacing the material of the housing wall in thedirection indicated by arrow W (in a direction away from the housingcentral axis and into the housing wall) as the tool is inserted into thehousing interior from an end thereof in direction V1. The portion 12 zof the displaced housing wall material along the exterior of the housingwall flows in direction W and into a cavity C100 of an associatedshaping die D100.

In the embodiments described herein, the end of at least one of the ventgrooves formed in the housing 12 extends to the end of body portion 12 csuch that an end of the vent groove is open at one of the housing ends12 a or 12 b. Thus, the interior of the housing is able to vent to anexterior of the housing at this location.

In an alternative method of forming a groove or a portion of a groove,the housing 12 is positioned so that its length extends along and restson a longitudinal base, with a portion of the housing exterior that willreside opposite the internal groove 12 v being positioned over a shapingdie cavity (such as cavity C100 described above). A press tool is theninserted into an end of the housing. The press tool has a groove formingportion shaped to produce a groove or grove portion having a desiredshape (including depth and width) and length when the groove formingportion is pressed into the surface of the interior of housing wall 12d. The groove forming portion of the tool is pressed into the wall 12 din a direction perpendicular to longitudinal axis L1 of the housing 12,thereby forming the groove and deforming a portion of the housing walloutwardly into the shaping die cavity as previously described. Usingthis method, different portions of the groove can be formed to havedifferent cross-sectional areas along planes taken through housing 12perpendicular to axis L1. This enables the cross-sectional area of theportion of the groove through which the gas flows around the resilientseal 40 to be controlled at any point along the groove (as seen forexample, in FIGS. 9-13). This method also enables formation of a groovethat is spaced from either end of the housing 12.

In another alternative method, groove 12 v is formed by a broachingoperation performed on the housing wall interior surface. In a knownmanner, the broaching operation removes a desired amount of materialfrom the wall interior surface, thereby reducing the thickness t of thehousing wall opposite the groove.

In another alternative method of forming a groove or a portion of agroove, housing 12 is formed from a suitable polymer. Any of grooves 12v may be formed by one of the methods previously described, or thegroove(s) may be formed, for example, by molding an insert fabricatedinto a desired groove profile shape (for example, one of the grooveshapes shown herein) into a wall of the polymeric housing. The insertmay then be removed from the groove formed into the housing wall afterthe molded housing has cooled to a sufficient degree.

FIG. 20 is a cross-sectional view of a portion of a housingincorporating an exemplary vent groove 12 v′, showing the basicprinciple of operation of the embodiments described herein. The drawingshows piston-mounted seal 40 progressing in direction V along housinginner surface 12 w from its pre-activation position, after activation.In position 1, the seal has not yet reached the groove 12 v′. Thus gaseson higher pressure side P1 are prevented by the seal from reaching thelower pressure side P2 of the piston by contact between the seal and thehousing wall inner surface 12 w. In position 2, after the seal 40 haspassed end 12 v′-a of groove 12 v′, the gases on the P1 side of thepiston have a route along the groove and around the seal to the lowerpressure side P2 of the piston. The gases continue to flow along thevent groove 12 v′ as shown by arrow Z, until the seal reaches groove end12 v′-b. In position 3 of the seal, the seal has passed groove end 12v′-b, the groove no longer resides below or outside of the seal. Thus,the gas flow path through the groove is blocked.

The fluid flow rate along the groove (and thus, the actuator forceprofile) is controlled by controlling the cross-sectional dimensions ofthe groove ends and the portions of the groove between the ends. Theseparameters may be varied at various locations along the groove asdescribed herein, in order to achieve a desired force profile.

FIG. 20A shows the particular embodiment 12 v of a vent groove shown inFIGS. 1-6, which extends from one end of the constant internal radiusportion of the housing along inner wall 12 w for at least part of thelength of the housing. In the embodiment shown, groove 12 v intersectsand is open at plane s1 near housing first end 12 a. The groove 12 vextends into and along wall 12 w for a portion of the length of thehousing between planes s1 and s2. It is seen that venting occurs alonggroove 12 v from the time motion of piston 30 is initiated (through sealpositions 1 and 2 as shown), until the seal reaches groove end 12 v-b.In position 3 of the seal, the seal has passed groove end 12 v′-b, thegroove no longer resides below or outside of the seal. Thus, the gasflow path through the groove is blocked.

The fluid flow rate along the groove (and thus, the actuator forceprofile) is controlled by controlling the cross-sectional dimensions ofthe groove ends and the portions of the groove between the ends. Theseparameters may be varied at various locations along the groove asdescribed herein, in order to achieve a desired force profile.

The actuator force profile (defined herein as the force exerted by thepiston rod 50 on an element connected thereto as a function of time) maybe controlled by controlling structural features of the actuator, suchas the number of vent grooves, the areas of the vent groove(s) (definedfor each vent groove as the area bounded by the seal 40 sliding over thegroove and the portion of the housing wall 12 d defining the edge of thegroove at any given cross-section of the housing, shown, for example, asarea A in FIG. 3), the length(s) of the vent grooves, the gas outputcharacteristics of the gas generator, and other pertinent factors. Thedimensions of these features can be modified to control suchcharacteristics as the total flow rate of gases along the vent groovesand the amount of time venting is enabled.

For example, in the embodiment shown in FIGS. 1-6, because groove 12 vextends outside or beyond remainder of the housing wall interior surface12 w, the groove 12 v provides a flow path (or vent) for pressurizedgases past the seal 40, from the higher pressure side P1 to the lowerpressure side P2, when the seal is positioned over the vent groove asshown in FIG. 20A. Gases flowing along the groove 12 v to the lowerpressure side of the piston 30 are then free to flow out of the housingthrough housing opening 12 f.

Venting through a portion of the groove is enabled under seal 40 as longas the groove extends to both the higher pressure side P1 of the seal 40and the lower pressure side P2 of the seal. Stated another way, in theembodiments described herein, venting along a groove will be enabled aslong as a gas flow passage exists along the groove and past the seal 40,from the higher pressure piston side P1 to the lower pressure side P2.

In embodiments described herein, the length and position of a ventgroove may be specified such that the venting is enabled along only aportion of the stroke length of the piston. In such embodiments, flow ofa portion of the generated gases along the vent and past seal 40 wouldbe enabled only for a portion of the piston stroke corresponding to thelength and position of the vent groove. In other embodiments of thegroove, the length and position of a vent groove may be specified suchthat the venting is enabled along the entire length of the constantinternal radius portion of the housing (i.e., along basically the entirestroke length of the piston).

In particular embodiments, the positions of the ends of a groove (orgrooves) may be specified so as to control the point in the pistonstroke at which the onset and/or end of venting occurs. For example, theactuator housing embodiment shown in FIGS. 1-6 includes a groove 12 vstructured to enable venting to commence at the start of the pistonstroke and along the portion of housing 12 along which vent 12 vextends. Groove first end 12 v-a is thus located so as to enable ventingat the start of the piston stroke. After the seal 40 passes an oppositeend 12 v-b of the groove, further groove venting is disabled until thepiston reaches the end 12 b of the housing. FIG. 8 is a plan view of theactuator embodiment shown in FIGS. 1-6.

FIG. 4 shows a side cross-sectional side view of the housing embodimentshown in FIGS. 1-3. In a particular embodiment of the housing. In thisembodiment, the groove 12 v is formed along the length of the housingsuch that groove end 12 v-b is a distance H of 30 millimeters from aninterior surface of housing endwall 12 g. Also, in this particularembodiment of the actuator, groove end 12 v-a is located along plane s1.

In the embodiment shown in FIGS. 1-6, a single groove 12 v isincorporated into the housing. Venting is enabled starting at groove end12 v-a and is enabled all the way until the piston reaches 12 v-b, at anopposite end of the groove.

In other embodiments, multiple vent grooves may be spaced apart alongthe housing wall interior surface. For example, FIGS. 7, 7A, 9, 14, 14A,15 and 16 show schematic views of actuator housings having multiplespaced apart grooves, 12 v-1 and 12 v-2.

FIG. 7 shows a plan cross-sectional view of a portion of an actuatorhousing having two diametrically opposed vent grooves 12 v-1 and 12 v-2.FIG. 7A shows a schematic view of a housing incorporating the ventgroove arrangement shown in FIG. 7. In a particular embodiment, grooves12 v-1 and 12 v-2 have equal lengths and are coextensive along thehousing (i.e., the beginnings of the grooves are located along a commonplane s1 extending perpendicular to the housing longitudinal axis L1,and the ends 12 v-1 b and 12 v-2 b of the grooves are located alonganother common plane s3 extending perpendicular to the housinglongitudinal axis L1 and located spaced apart from the first plane).Thus, in this embodiment, venting through both grooves commences at thesame time and ends at the same time as the piston travels in directionV.

In any embodiment incorporating multiple grooves, each groove may haveany desired length and relative position along the length of housing 12.That is, the grooves may or may not have the same lengths, and may ormay not be coextensive with each other, according to the actuation forcerequirements of a particular application. Also, any desired number ofvent grooves may be employed. In addition, although the grooves 12 v-1and 12 v-2 are angularly spaced apart 180°, the angular spacing(s)and/or other distances between any pair of grooves in any set of groovesmay be equal or unequal.

Any desired number of vent grooves may be employed. In addition, theangular spacing(s) and/or other distances between pairs of grooves inany set of grooves may be equal or unequal. In addition, the length andposition of any vent groove may be specified such that the venting isenabled along only a portion of the stroke length of the piston or alongthe full length of the piston stroke. In such embodiments, flow of aportion of the generated gases along the vent and past seal 40 would beenabled only for a portion of the piston stroke corresponding to thelength and position of the vent groove.

FIG. 14 shows a plan cross-sectional view of a portion of an actuatorhousing having three angularly equally spaced vent grooves 12 v-1, 12-v2 and 12 v-3. FIG. 14A shows a schematic view of a housing incorporatingthe vent groove arrangement shown in FIG. 14. In the embodiment shown inFIGS. 14 and 14A, grooves 12 v-1, 12-v 2 and 12 v-3 all have equallengths and are coextensive. Groove ends 12 v-1 a, 12 v-2 a and 12 v-3 aintersect plane s1, while opposite groove ends 12 v-1 b, 12 v-2 b and 12v-3 b intersect a plane s3 located between planes s1 and s2 andextending perpendicular to axis L1.

Another embodiment (shown in FIG. 15) includes at least two grooves 12v-1 and 12 v-2 with overlapping ends. Thus, in the embodiment shown inFIG. 15, a portion of first groove 12 v-1 extends between a third planes3 and a fourth plane s4 located between the first and second planes s1and s2. Also, a portion of second groove 12 v-2 extends between thethird and fourth planes. Groove 12 v-1 is structured to enable ventingto commence at a point 12 v-1 a on the groove at the start of the pistonstroke. Venting is enabled through the groove 12 v-1 until the sealpasses 12 v-1 b, which is the end of groove 12 v-1. However, duringpassage of the seal from point 12 v-1 a to 12 v-1 b along groove 12 v-1,the seal passes over point 12 v-2 a along groove 12 v-2 (at the end ofgroove 12 v-2 closest to plane s1), thereby enabling venting alonggroove 12 v-2 as well as along groove 12 v-1. Venting is now enabledalong both grooves until the seal 40 passes point 12 v-1 b along groove12 v-1, after which venting is enabled only along groove 12 v-2 untilthe end 12 v-2 b of this groove.

Although FIG. 15 shows an the embodiment having one pair of overlappinggrooves, any number of overlapping grooves may be employed as needed toachieve a desired actuation force profile. For example, a single firstgroove enabling venting during a first portion of the piston stroke mayoverlap with multiple second grooves, in the manner shown in FIG. 15, toenable venting through these second grooves in a later portion of thepiston stroke. Similarly, multiple first grooves enabling venting duringa first portion of the piston stroke may overlap with a single secondgroove, in the manner shown in FIG. 15, to enable venting through thissecond groove in a later portion of the piston stroke.

Another embodiment (shown in FIG. 16) includes at least two grooves 12v-1 and 12 v-2 having central longitudinal axes arranged along a commonplane X′ extending through central axis L1, with a space D′ betweenadjacent ends of the grooves. Longitudinal axes of both grooves liealong the plane X′ which extends from the housing longitudinal axis L1to a side of the housing, as shown in FIG. 16. In the particularembodiment shown in FIG. 16, grooves 12 v-1 and 12 v-2 are coaxial.grooves Groove 12 v-1 is structured to enable venting to commence at apoint 12 v-1 a at the start of the piston stroke. Venting is enabledthrough the groove until the seal passes 12 v-1 b, which is the end ofgroove 12 v-1 and intersects a plane s3 extending perpendicular to axisL1. Venting is then disabled until the seal reaches end 12 v-2 a ofgroove 12 v-2 which is an end of groove 12 v-2 intersecting anotherplane s4 spaced apart from plane s3 and extending perpendicular to axisL1. Venting is then enabled along groove 12 v-2 until end 12 v-2 b ofgroove 12 v-2 is reached.

In the embodiment shown in FIG. 17, a single vent groove 112 v similarto that shown in FIGS. 1-2 is formed so as to extend from the second end12 b of the housing 12, rather than from the first end 12 a of thehousing. Venting along this groove is enabled when the piston seal 40reaches groove end 112 v-a, which intersects a plane s3 extendingperpendicular to axis L1. If desired, multiple vent grooves can beformed extending from housing second end 12 b, in a manner similar tothat shown in FIG. 14A.

In the embodiment shown in FIGS. 1-6, groove 12 v has a constantcross-sectional area (within the limits of manufacturing tolerances)along its entire length. In any of the embodiments described herein, thegrooves (where multiple grooves are incorporated into the housing) mayhave the same cross-sectional areas or different cross-sectional areas.

In addition, the cross-sectional area of any particular groove may bevaried along its length as another means of affecting the actuator forceprofile. Control of the area through which the gases may flow enables acontrolled variation of the gas flow or venting rate as the pistontravels along the groove.

For example, in the embodiment shown in FIG. 9, the depth d′ of groove112 v varies along the length of the groove. This variation in groovedepth d′ produces a corresponding variation in groove cross-sectionalarea along the length of the groove. In the embodiment shown in FIG. 9,the groove 112 v is tapered so that the depth d′ of the groove varies ata uniform rate along the length of the groove. However thecross-sectional area of the groove can be varied in any desired mannerthat can be fabricated.

In addition (or alternatively), the forming tool may be formed so as tovary the width of the tool therealong. This enables the width of agroove formed in the housing wall to be correspondingly varied duringfabrication of the housing.

In other embodiments, any groove may be formed into adjacent portions orsections into “zones” having different characteristics. For example, inthe embodiments shown in FIGS. 10 and 11, a first portion R1 of thegroove 112 v has a constant cross-sectional area, and a second portionR2 of the groove adjacent the first portion has a cross-sectional areawhich varies along the length of the groove.

In the embodiment shown in FIG. 12, a first portion R1 of the groove 112v has a first constant cross-sectional area, and a second portion R2 ofthe groove adjacent the first portion has a second constantcross-sectional area different from the first cross-sectional area.

In the embodiment shown in FIG. 13, a first portion R1 of the groove 112v has a cross-sectional area which varies along the length of thegroove, and a second portion R2 of the groove has a cross-sectional areawhich varies along the length of the groove.

In view of the above, it may be seen that numerous options exist forproviding any of a wide variety of actuator force profiles, using themethods and structures described herein.

During operation of the actuator, the gas generator or other pressurizedgas source is activated to introduce pressurized gas into the housing onthe higher-pressure side P1 of the piston. The pressurized gas forcesthe piston in the negative V (−V) direction, whereby a force is exertedby piston rod 50 on an element or mechanism attached thereto. Theactuator force profile will be related to the amount of pressurized gasvented through the groove(s) from the higher pressure side P1 of thepiston to the lower pressure side P2. At the end of the piston strokeand/or when the seal has passed the groove(s) and is in flush contactwith ungrooved surfaces of the housing wall, the gasses remaining in thehigher pressure side can continue to escape to some degree from thehigher-pressure area to the lower pressure area between the housing walland the seal until the pressure in the higher-pressure area is nearlyequalized with atmospheric pressure. The result is a fully depressurizedactuator within seconds of actuator deployment.

Also, in a particular embodiment, prior to activation of the actuator,the piston 30 is positioned such that a portion of at least one ventgroove resides on both the higher pressure side P1 (i.e., the gasgenerator side) and the lower pressure side (i.e., the side of thepiston on which the piston rod 50 exits the housing 12) of the seal 40.This enables the housing internal pressures on sides P1 and P2 of thepiston to be equalized during assembly of the actuator and prior toactuator activation.

FIG. 18 shows a plot of force exerted by the piston rod vs. displacementof the piston in the negative V direction in the drawings for theembodiment shown in FIGS. 1-6, after the actuator has been fullydeployed (i.e., at maximum travel of the piston). As seen from FIG. 18,as the piston rod 50 is pressed back into the housing, the forceresisting displacement of the piston 30 in the −V direction steadilyincreases until the piston seal 40 reaches a point just past point 12v-b along the groove 12 v. At this point, venting of the pressurized gasstored on side P1 of the piston is once again enabled. The gas ventsthrough groove 12 v, thereby causing the rapid drop in force resistingfurther movement of the piston in the −V direction, as shown in FIG. 18.

Referring now to FIGS. 21A-22B, in another embodiment 12 k of a ventgroove, the length of the groove extends along an axis K residing on aplane that is perpendicular to housing axis L1. The cross-sectionaldimensions of the groove may be controlled to provide a relatively rapidor “pulsed” release of gas of a desired amount, from high pressure sideP1 to lower pressure side P2, as the seal 40 passes over the groove. Thegroove 12 k may extend along 360 degrees of the surface of wall 12 w,thereby forming a continuous “ring”, as shown in FIGS. 22A and 22B.Alternatively, the groove 12 k may extend along only a specific portionor included angular extent M of the surface 12 w, as shown in FIGS. 21Aand 21B. These variations enable increased flexibility in control of theactuator force profile. The groove 12 k may be formed using one of thegroove formation methods described herein.

FIG. 23 is a schematic view of a portion of a pedestrian protectionsystem 900 installed in a vehicle 880 and incorporating a hood-liftingdevice 10 in accordance with an embodiment described herein. In thisembodiment of the pedestrian protection system 900, a vehicle mountedsensor 810 detects contact between the vehicle and a pedestrian (notshown). Responsive to this detected contact, an activation signal issent to the hood-lifting mechanism 10, resulting in activation of thegas generator or otherwise releasing pressurized gases into the interiorof housing 12 to produce extension of the piston rod 50 from thehousing, as previously described. The extending piston rod 50 thenraises the portion of the hood 902. The hood-lifter activation signalmay be sent from the sensor 810 or from a suitably-configured controller(not shown) which receives the vehicle-pedestrian contact signal fromsensor 810 and generates the activation signal in response thereto.

It will be understood that the foregoing descriptions of the variousembodiments are for illustrative purposes only. As such, the variousstructural and operational features herein disclosed are susceptible toa number of modifications, none of which departs from the scope of theappended claims.

What is claimed is:
 1. A vented pressurized gas-powered actuatorcomprising: a housing having a central longitudinal axis and an innersurface, the inner surface having a constant radius between first planeand second planes extending perpendicular to the axis; and at least onevent groove extending from the inner surface in a direction away fromthe axis, the at least one groove having a first end intersecting thefirst plane.
 2. The actuator of claim 1 wherein the inner surfacedefines a cylindrical volume, and wherein the groove resides outside thecylindrical volume.
 3. The actuator of claim 1 wherein the at least onegroove has a second end opposite the first end and intersecting a thirdplane located between the first and second planes.
 4. The actuator ofclaim 1 further comprising another groove extending from the innersurface in a direction away from the axis.
 5. The actuator of claim 4wherein a longitudinal axis of the other groove resides on a plane thatis perpendicular to the housing longitudinal axis.
 6. The actuator ofclaim 4 wherein the other groove has a first end spaced apart from thefirst plane.
 7. The actuator of claim 6 wherein the other groove has asecond end spaced apart from the second plane, and wherein the othergroove second end is closer to the second plane than to the first plane.8. The actuator of claim 6 wherein the other groove has a second endintersecting the second plane.
 9. The actuator of claim 4 wherein theother groove is coaxial with the at least one groove.
 10. The actuatorof claim 4 wherein the other groove is positioned diametrically oppositethe at least one groove.
 11. The actuator of claim 4 wherein a portionof the at least one groove extends between third and fourth planeslocated between the first and second planes, and wherein a portion ofthe other groove extends between the third and fourth planes.
 12. Theactuator of claim 1 further comprising a gas generator, and a pistonmovably positioned within the housing, the piston having a cavity formedtherein along a side of the piston facing the gas generator.
 13. Avented pressurized gas-powered actuator housing comprising an innersurface and at least one vent groove extending from the inner surfaceinto the wall.
 14. The housing of claim 12 wherein the inner surface hasa constant radius, and wherein the at least one groove has a first endintersecting a first plane extending through the inner surface andperpendicular to a longitudinal axis of the at least one groove, and asecond end intersecting a second plane extending through the innersurface and perpendicular to a longitudinal axis of the at least onegroove.
 15. An actuator including a housing in accordance with claim 12.16. A vehicle including an actuator in accordance with claim
 12. 17. Avehicle including an actuator in accordance with claim 1.